Four more journalists have been charged with felonies after being arrested while covering the unrest around Donald Trump’s inauguration, meaning that at least six media workers are facing up to 10 years in prison and a $25,000 fine if convicted.

A documentary producer, a photojournalist, a live-streamer and a freelance reporter were each charged with the most serious level of offense under Washington DC’s law against rioting, after being caught up in the police action against demonstrators.

The Guardian learned of their arrests after reporting on Monday that the journalists Evan Engel of Vocativ and Alex Rubinstein of RT America had also been taken into custody by police and charged with felonies while covering the same unrest on Friday morning.

Jack Keller, a producer for the web documentary series Story of America, said that he was detained for about 36 hours after being kettled by police at 12th and L streets on Friday morning and then arrested despite telling officers that he was covering the demonstrations as a journalist.

“The way we were treated was an absolute travesty,” said Keller, whose cellphone has been kept by the authorities. Keller’s editor, Annabel Park, said: “It is a maddening and frustrating situation. These are people who were there observing and documenting.”

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Matt Hopard, an independent journalist who was live-streaming the Friday protests, was arrested at the same site as Keller, Engel and Rubinstein, according to metropolitan police records. He said in a message that he denied the charge against him.

Also arrested while covering the demonstrations at 12th and L streets were Shay Horse, an independent photojournalist and activist, and Aaron Cantú, a freelance journalist and activist, who has written for outlets including the Baffler, the Washington Spectator and the New Inquiry. Both deny wrongdoing.

In all, more than 200 people were arrested on Friday, after property was vandalized in the US capital in the hours around Trump’s swearing-in as president. Police said that six officers suffered minor injuries.

The National Lawyers’ Guild accused Washington DC’s metropolitan police department of having “indiscriminately targeted people for arrest en masse based on location alone” and said they unlawfully used teargas and other weapons.

“These illegal acts are clearly designed to chill the speech of protesters engaging in First Amendment activity,” Maggie Ellinger-Locke, of the guild’s DC branch, said in a statement.

None of the arrest reports for the six journalists makes any specific allegations about what any of them are supposed to have done wrong. Keller’s report, which also covers the arrests of an unknown number of unidentified other people, includes a note that a police vehicle was vandalized. “I had absolutely nothing to do with the vandalism,” said Keller.

Reports on the arrests of five of the six journalists contain identical language alleging that “numerous crimes were occurring in police presence”. They state that windows were broken, fires were lit and vehicles were damaged. “The crowd was observed enticing a riot by organizing, promoting, encouraging and participating in acts of violence in furtherance of the riot,” the police reports said.

The US attorney’s office for Washington DC, which is prosecuting those arrested, declined to comment on the journalists’ specific cases but said it was continuing to review evidence from the day with the police.

“Based on the facts and circumstances, we determined that probable cause existed to support the filing of felony rioting charges,” William Miller, a spokesman for the office, said in a statement. “As in all of our cases, we are always willing to consider additional information that people bring forward.”